1. Field of the Invention
The present invention relates to an apparatus for capturing a connecting T channel to be measured, when the channel connecting a parent telephone with a daughter telephone, the frequencies, the signal levels, modulation factor and so forth are to be measured for a cordless telephone.
2. Description of the Prior Art
At the time of adjustment and testing during manufacture or repair of a cordless telephone, it is necessary to determine which channel connects the parent and the daughter phones of a cordless telephone. For this purpose, an apparatus for quickly capturing a channel to be measured for a cordless telephone has been developed.
The following is an outline of the system of a low power type cordless telephone which will be described so that a conventional apparatus for capturing a channel to be measured may be readily understood. With regard to the frequency band to be applied, the 250 MHz band is used for transmission from a parent phone to a daughter phone and the 380 MHz band is used for transmission from a daughter phone to a parent phone. For each band, 89 channels are provided, and 87 channels out of the 89 channels are used as channels for communication and the remaining two channels are used as control channels. The relation between the channels for both parent and daughter phones is already decided in such a manner as that the connecting channel from a daughter phone to a parent phone may be determined once the connecting channel from a parent phone to a daughter phone is established.
According to such a cordless telephone system as described above, adjustment is made in such a way that, before the phones, that is a parent phone and a daughter phone, are connected to each other, a control code sent from one phone by way of a predetermined control channel is received and interpreted by the other phone. The reception tuned condition is so shifted from the control channel that the channel designated by the control code can be brought into a receptive condition, whereby a communication is received by way of the designated channel. Then, if the reception level at the designated channel of the other phone is below a specified level, connection is made by way of the designated channel. On the other hand, however, if the reception level at the designated channel of the other phone is above a specified level, a decision is made that the designated channel is already occupied by a signal of another phone, such that the reception tuned condition of the other phone is returned to the control channel. Then the one phone sends to the other phone by way of the control channel a code designating a different channel. Such operations are repeated until the phones are finally connected by way of a channel having a reception lever below a specified lever.
An example of a conventional cordless telephone tester or apparatus for capturing a channel to be measured, adapted to detect which channel is currently connecting the parent phone and the daughter phone which are to be tested in a cordless telephone system constituted as explained above is configured as shown in FIG. 1. As shown in FIG. 1, the apparatus for capturing a channel to be measured comprises various elements other than a reception measuring circuit 10. The channel signal which has been sent from a cordless telephone and received in the apparatus for capturing a channel to be measured is converted to an intermediate frequency f.sub.1 by a frequency converter 14 which has received a local oscillation signal from a local oscillator 12 which is a voltage controlled osciliator. The converted channel then passes through a one-channel band pass filter 16 which allows only one channel having a central frequency of f.sub.1 to be passed and amplified by an intermediate frequency amplifier 18. The signal which is contained in the amplified channel is then sent to a signal intensity sequential comparing circuit 20. The signal intensity sequential comparing circuit 20 includes a signal level detector 22, a level comparator 24 and a memory 26. The signal level detector 22 is adapted to detect the level of a signal sent from the intermediate frequency amplifier 18 and send the detected level to the level comparator 24. The level comparator 24 is adapted to compare the signal level of the other channel which was previously detected and stored in the memory 26, with the signal level which has been sent from the signal level detector 22 and to store in the memory 26 the higher signal level along with the channel corresponding thereto A data processing device 28 is adapted to read out the stored channel and the relative detected signal level and select the channel, the signal level of which is the highest, or capture the channel to be measured and send the signal representing the channel in question to a frequency control unit 30. When an electromagnetic wave having a frequency corresponding to the channel indicated by the signal received from the data processing unit 28 is received and the frequency converted, the frequency control unit 30 applies a required voltage to the local oscillator 12 in order to cause the local oscillator 12 to oscillate in a manner that the intermediate frequency after frequency conversion becomes f.sub.1. In this way, the frequency control unit 30 is furthermore adapted to sequentially provide the local oscillator 12 with each voltage corresponding to each channel in a manner that the local oscillator 12 performs a frequency sweep, in order to cause the frequency converter 14 to convert frequencies of the control channel and the communication channel which have been received, sequentially into intermediate frequencies of f.sub.1. It is to be noted that the reception measuring circuit 10 serves as a circuit for measuring the signal level, modulation factor, etc. of the cordless telephone to be tested after the channel to be measured has been captured as explained above, so that it is not directly related to the present invention.
As explained above, an apparatus for capturing a channel to be measured according to the prior art is adapted to detect sequentially tile signal levels for all channels of both control channels and communication channels of a cordless telephone to be measured, and then sequentially compare the intensity of signals to store the signal level which is the highest. As a consequence, since the apparatus decides and captures the highest reception channel after comparisons of all channels have been completed, a lot of time, generally, from several seconds to several tens of seconds, is required for the operation of capturing of the channel to be measured.
Furthermore, since a considerable time has been required as described above, it was impossible for conventional apparatus to capture a control channel when a cordless telephone is in the state of transmission before a parent phone and a daughter phone are connected via a connecting channel.